The subject of noise pollution has become a critical issue in recent years and has had a very significant impact on the earthmoving industry. Rigid sound requirements for equipment have been adopted worldwide, resulting in extensive modifications to vehicles in an attempt to reduce the noise produced during their operation. Obviously, one of the primary sources of noise emanates from the engine of the vehicle. The most logical way to reduce the noise is to encase the engine in an enclosure that is lined with acoustical foam or other sound absorptive material. While this solution appears simple enough, one must remain aware of the cooling requirements for the engine and other powertrain components such as torque converters, hydraulic pumps, etc., whose heat exchangers are cooled by air passing through the engine's enclosure. It is not uncommon for the ventilation air moving through an engine enclosure of an earthmoving vehicle to pick up a heat load equivalent to approximately 20% of the output power. Therefore it is an absolute necessity to provide openings in the enclosure of sufficient size to not only reduce the temperature of the components within the enclosure but to also provide a flow of air through a radiator and various heat exchangers to cool fluid that is circulated internally through the engine and related components.
This flow of air has conventionally been provided by an axial fan that is positioned behind, or in front of, the radiator and heat exchangers to draw ambient air from outside the enclosure through the enclosure and the fluid cooling devices. Arrangements of this type have been used successfully to attenuate a large portion of the noise that escapes from an engine enclosure. However, as the noise requirements have become more stringent, problems with this method of noise attenuation have been encountered. A logical solution to the more stringent requirement is to increase the amount of sound absorptive material within the enclosure and to reduce the number and/or size of openings in the enclosure through which noise may escape. When this happens, the flow of cooling air into the enclosure is reduced to a point of inadequacy. Not only is the flow of air that is passed by the fluid cooling devices reduced, but the flow of air through the enclosure itself is reduced which results in an overall increase in temperature within the compartment. This adversely affects many temperature sensitive components, such as the alternator, the fuel injection system and various electronic components such as microprocessors that have been incorporated into the operation of an engine through modern day engine technology. To increase the flow of air, it has been common practice to provide a fan that will rotate at a greater speed. While this solution has achieved moderate success, conditions have reached a point where the fan speed requirements are so great that the noise created by the fan has surpassed the engine as the dominant noise source, particularly at high idle with an engine driven fan.
The next step in the evolution of the sound suppressed engine compartment resulted in the separation of the radiator and fluid cooling devices, including the fan, from the engine and its related components. One such design is disclosed in U.S. Pat. No. 3,866,580 issued to Whitehurst et al. The design of Whitehurst provides a wall between the fluid cooling components and the engine related components. Ambient air outside the enclosure is drawn through openings in the side and top of the enclosure by an engine driven fan. The flow of air passes through the fluid cooling components that are positioned on the engine side of the fan. The enclosure is ventilated by ambient air that is drawn from air inlets positioned at the rear and sides of the vehicle by a pressure differential created by the relationship between the engine exhaust pipe and the enclosure exhaust stack. As exhaust gasses are expelled from the engine into the exhaust stack, a pressure differential or a “venturi effect” is created that draws air through the engine enclosure. This requires relatively large openings in the engine compartment, however, to provide adequate air flow; and thus, highly efficient noise attenuation is sacrificed. Also, the flow of air is not controllable and is only effective while the engine is running. With a tightly sealed, sound suppressed engine enclosure, the temperature rise experienced within the enclosure after engine shut down can result in premature failure of temperature sensitive components such as microprocessors.
Another design that discloses separated compartments for the engine related components and the fluid cooling components is disclosed in U.S. Pat. No. 4,086,976 issued to Holm et al. Holm is similar in function to Whitehurst in the method of ventilating the two compartments. A flow of ambient air is drawn through the fluid cooling components by an engine driven fan, and the engine compartment is ventilated via a similar pressure differential created by the flow of exhaust gasses from an exhaust pipe of the engine. A conduit extends between the engine compartment and the compartment housing the engine driven fan so that the fan may also be utilized to ventilate the engine compartment. This design exhibits the same deficiencies discussed with respect to the Whitehurst design. Additionally, since a fan is a volumetric flow device and the airflow through the conduit enters the fan inlet air stream, the fan speed must be increased above that speed sufficient to satisfy the fluid cooling device airflow requirements, thereby resulting in a fan noise penalty.
Yet another design that utilizes separate compartments between the engine and related drive component and the fluid cooling components is disclosed in U.S. Pat. No. 4,854,278 issued to Honecker, and U.S. Pat. No. 5,692,467 issued to Sahm et al. This design utilizes a fan in the fluid cooling compartment to draw air from openings in the front of the vehicle, through the engine compartment and into the fluid cooling compartment. The air from the engine compartment is then mixed with ambient air drawn in through the top of the fluid cooling component compartment upstream from the radiator and heat exchangers. Again the design exhibits many of the deficiencies pointed out with respect to the designs described above. Additionally, it must be noted that the heated air from the engine compartment will increase the overall temperature of the air drawn through the fluid cooling devices. Since the performance of a heat exchanger is proportional to the difference in inlet temperature between the air and the fluid, cooling efficiency is sacrificed.
The present disclosure is directed to overcoming one or more of the problems or disadvantages existing in the prior art.